The fossils at Dinosaur Park come from a time called the Cretaceous period, which lasted from 145 to 65 million years ago. This is relatively recent history compared to the 4.5 billion year age of the Earth, but is still long before the nearby marine deposits of Calvert County were formed (20 million years ago) or the earliest humans appeared on Earth (200 thousand years ago).

In many ways, the Cretaceous period marked the birth of the modern world. During this time, the northern and southern landmasses of the prior period began to break up, forming the mosaic of continents and oceans we know today. The expanding oceans influenced the global climate, which became cooler and drier, with more pronounced seasons. This in turn led to the expansion of temperate forests, with trees such as oak, hickory and magnolia gaining prominence throughout North America. Meanwhile, flowering plants first became widespread in the Cretaceous period, joined by the first pollinating insects. The fossils found at Dinosaur Park help scientists understand how and why these important environmental transitions took place.

115 million years ago, Prince George’s County was a flat coastal plain with winding rivers. The environment probably resembled parts of southern Louisiana today. Sharp bends in the rivers became detached and formed lakes or swamps called oxbows. Dinosaur Park is a remnant of one such oxbow.

A fossil is any evidence of past life. Fossils are as diverse as the living things that left them behind, and can range from microscopic plant pollen to giant dinosaurs.

Most organisms die and decay, leaving no remains behind, but in rare circumstances a dead organism can become fossilized. Fossils are primarily found in sedimentary rock, which is formed on the Earth’s surface. Layers of sedimentary rock are formed by accumulating particles like sand or silt. Sometimes, plants and animals become buried in this sediment, which protects them from scavengers, organic decay, or weathering. Once buried, water carrying dissolved minerals may flow through the remains, leading them to be preserved at the cellular level. Find more information about fossils.

Most animal fossils are found as isolated bones and teeth, rather than complete skeletons. The missing bones might have been destroyed by predators or scavengers as they fed on the animal, swept away by floods, fractured under heavy sediments after burial, or broken while eroding out of the ground. However, scientists familiar with skeletal anatomy can still identify isolated or fragmentary fossils.